Method and materials for calibrating flow cytometers and other analysis instruments

ABSTRACT

A method for calibrating an instrument for using that instrument to obtain at least one light-related signal from particles under analysis comprises directing an incident beam of light at calibration particles having one or more known characteristics related to the particles expected to be analyzed. Both a light signal and a noise signal from the calibration particles are detected. A measurement is made of the ratio of the detected light signal to the detected noise signal, and that measurement is reported. The measured ratio is then compared to a predetermined ratio which represents a threshold for minimum instrument performance. This method further includes adjusting, if the predetermined ratio has not been attained, the operation of the instrument, while the calibration particles are within the incident beam of light, until the measured ratio reaches the predetermined ratio whereby the instrument is calibrated for subsequently obtaining the light signal from particles to be analyzed. A kit of reagents for use in calibrating an instrument for performing two-color analysis of particles and particle standards for calibrating fluorescence analysis instruments are also part of the instant invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for calibrating an instrument used to analyze particles, and more particularly, concerns a method and materials for calibrating flow cytometry instruments prior to using such instruments for obtaining at least one light-related signal from particles passing through the instrument.

2. Background Description

There are a number of commercially available instruments used for particle or cellular analysis. Characteristics of particles, particularly biological particles or cells, may be determined by techniques in which the particles remain relatively fixed while being analyzed or while the particles are moving in a stream or carried in a suspension. Flow cytometers are known and available for analyzing or detecting certain characteristics of particles which are in motion. In typical flow cytometry instruments, cells or other biological particles are caused to flow in a liquid stream so that each particle, preferably one at a time, passes through a sensing region which measure physical or chemical characteristics of the particles. Although a variety of signals may be detected for association with different characteristics of the particles, including electrical, acoustical and radioactive, flow cytometers commonly rely on opticald. Instead of monomers 1a and 2a, 61.1619 g (0.28706 mol) of monomer 1b is dehydrochlorinated in an "initial" solution of 338.4 g PPA having a P₂ O₅ content of 77.2% (prepared by mixing 101.5 g of 85.4% H₃ PO₄ with 236.8 g of 115% PPA). When dehydrochlorination is substantially complete, 69.5488 g (0.28706 mol) of monomer 2j is added followed by the gradual addition of 140.1 g of P₂ O₅. The mixture is then stirred and heated essentially according to Example 8. The amount of P₂ O₅ is preselected (as determined in accord with the aforementioned formulae a* and b*) to provide the reaction mixture with an effective P₂ O₅ content of approximately 83.8% prior to the start of polymerization and an effective P₂ O₅ content of approximately 82.2% subsequent to substantial complete polymerization. The reaction product obtained exhibits stir-opalescence and is further characterized as having a polymer concentration of 17%; fibers are readily formed by direct spinning, or drawing from the reaction product. The polymer obtained is of the following structure:

    --AB--.sub.n

characterized by an intrinsic viscosity of 16 dL/g in MSA at 30° C. which corresponds to an n value of average polymerization of about 60.

EXAMPLE 18

The procedure of Example 8 is essentially repeated. Instead of monomers 1a and 2a, 81.9923 g (0.28869 mol) of monomer 1c is dehydrochlorinated in an "initial" solution of 366.8 g PPA having a P₂ O₅ content of 77.2% (prepared by mixing 110 g of 85.4% ₃ PO₄ with 256.8 g of 115% PPA). When dehydrochlorination is substantially complete. 69.9438 g (0.28869 mol) of monomer 2j is added followed by the gradual addition of 148.4 g of P₂ O₅. The mixture is then stirred and heated essentially according to Example 8. The amount of P₂ O₅ is preselected (as determined in accord with the aforementioned formulae a* and b*) to provide the reaction mixture with an effective P₂ O₅ content of approximately 83.8% prior to the start of polymerization and an effective P₂ O₅ content of approximately 82.2% subsequent to substantial complete polymerization. The reaction product obtained exhibits stir-opalescence and is further characterized as having a polymer concentration of 16%; fibers are readily formed by direct spinning, or drawing from the reaction product. The polymer obtained is of the following structure:

    --AC--.sub.n

characterized by an intrinsic viscosity of 16 dL/g in MSA at 30° C. which corresponds to an n value of average polymerization of about 60.

EXAMPLE 19

The procedure of Example 8 is essentially repeated. Instead of monomers 1a and 2a, 93.8232 g (0.29202 mol) of monomer 1i is dehydrochlorinated in an "initial" solution of 263.5 g PPA having a P₂ O₅ content of 77.2% (prepared by mixing 79.1 g of 85.4% H₃ PO₄ with 184.4 g of 115% PPA). When dehydrochlorination is substantially complete, 48.5129 g (0.29202 mol) of monomer 2a is added followed by the gradual addition of 171 g of P₂ O₅. The mixture is then stirred and heated essentially according to Example 8. The amount of P₂ O₅ is preselected (as determined in accord with the aforementioned formulae a* and b*) to provide the reaction mixture with an effective P₂ O₅ content of approximately 86.2% prior to the start of polymerization and an effective P₂ O₅ content of approximately 82.2% subsequent to substantially complete polymerization. The reaction product obtained exhibits stir-opalescence and is further characterized as having a polymer concentration of 18%; fibers are readily formed by direct spinning, or drawing from the reaction product. The polymer obtained is of the following structure:

    --LI--.sub.n

characterized by an intrinsic viscosity of 15 dL/g in MSA at 30° C.

EXAMPLE 20

The procedure of Example 8 is essentially repeated. Instead of monomers 1a and 2a, 93.1836 g (0.32225 mol) of monomer 1j is dehydrochlorinated in an "initial" solution of 254.0 g PPA having a P₂ O₅ content of 77.2% (prepared by mixing 76.2 g of 85.4% H₃ PO₄ with 177.8 g of 115% PPA). When dehydrochlorination is substantially complete, 53.5357 g (0.3225 mol) of monomer 2a is added, followed by the gradual addition of 178.4 g of P₂ O₅. The mixture is then stirred and heated essentially according to Example 8. The amount of P₂ O₅ is preselected (as determined in accord with the aforementioned formulae a* and b*) to provide the reaction mixture with an effective P₂ O₅ content of approximately 86.6% prior to the start of polymerization and an effective P₂ O₅ content of approximately 82.2% subsequent to substantially complete polymerization. The reaction product obtained exhibits stir-opalescence and is further characterized as having a polymer concentration of 18%; fibers are readily formed by direct spinning, or drawing from the reaction product. The polymer obtained is of the following structure:

    --MI--.sub.n

characterized by an intrinsic viscosity of 14 dL/g in MSA at 30° C.

EXAMPLE 21

The procedure of Example 8 is essentially repeated. Instead of monomers 1a and 2a, 93.1836 g (0.32225 mol) of monomer 1k is dehydrochlorinated in an "initial" solution of 254.0 g PPA having a P₂ O₅ content of 77.2% (prepared by mixing 76.2 g of 85.4% H₃ PO₄ with 177.8 g of 115% PPA). When dehydrochlorination is substantially complete, 53.5357 g (0.32225 mol) of monomer 2a is added, followed by the gradual addition of 178.4 g of P₂ O₅. The mixture is then stirred and heated essentially according to Example 8. The amount of P₂ O₅ is preselected (as determined in accord with the aforementioned formulae a* and b*) to provide the reaction mixture with an effective P₂ O₅ content of approximately 86.6% prior to the start of polymerization and an effective P₂ O₅ content of approximately 82.2% subsequent to substantially complete polymerization. The reaction product obtained exhibits stir-opalescence and is further characterized as having a polymer concentration of 18%; fibers are readily formed by direct spinning, or drawing from the reaction product. The polymer obtained is of the following structure:

    --NI--.sub.n

characterized by an intrinsic viscosity of 14 dL/g in MSA at 30° C.

EXAMPLE 22

The procedure of Example 8 is essentially repeated. Instead of monomers 1a and 2a, 128.47 g (0.32431 mol) of monomer 11 is dehydrochlorinated in an "initial" solution of 223.5 g PPA having a P₂ O₅ content of 79.4% (prepared by mixing 44.7 g of 85.4% H₃ PO₄ with 178.8 g of 115% PPA). When dehydrochlorination is substantially complete, 53.8778 g (0.32431 mol) of monomer 2a is added, followed by the gradual addition of 197.0 g of P₂ O₅. Inorganic salts, such as lithium salts (e.g., LiCl, LiF, Lithium phosphate, and the like) can be added at this point, if required, to promote polymer solubility. The mixture is then stirred and heated essentially according to Example 8. The amount of P₂ O₅ is preselected (as determined in accord with the aforementioned formulae a* and b*) to provide the reaction mixture with an effective P₂ O₅ content of approximately 89.1 % prior to the start of polymerization and an effective P₂ O₅ content of approximately 82.2% subsequent to substantially complete polymerization. The reaction product obtained exhibits stir-opalescence and is further characterized as having a polymer concentration of 18%; fibers are readily formed by direct spinning, or drawing from the reaction product. The polymer obtained is of the following structure:

    --OI--.sub.n

characterized by an intrinsic viscosity of 12 dL/g in MSA at 30° C.

EXAMPLE 23

The procedure of Example 8 is essentially repeated. Instead of monomers 1a and 2a, 70.3707 g (0.21902 mol) of monomer 1i is dehydrochlorinated in an "initial" solution of 323.1 g PPA having a P₂ O₅ content of 77.2% (prepared by mixing 96.9 g of 85.4% H₃ PO₄ with 226.2 g of 115% PPA). When dehydrochlorination is substantially complete, 53.0654 g (0.21902 mol) of monomer 2j is added followed by the gradual addition of 125.0 g of P₂ O₅. The mixture is then stirred and heated essentially according to Example 8. The amount of P₂ O₅ is preselected (as determined in accord with the aforementioned formulae a* and b*) to provide the reaction mixture with an effective P₂ O₅ content of approximately 83.6% prior to the start of polymerization and an effective P₂ O₅ content of approximately 82.2% subsequent to substantially complete polymerization. The reaction product obtained exhibits stir-opalescence and is further characterized as having a polymer concentration of 18%; fibers are readily formed by direct spinning, or drawing from the reaction product. The polymer obtained is of the following structure:

    --AL--.sub.n

characterized by an intrinsic viscosity of 17 dL/g in MSA at 30° C.

EXAMPLE 24

The procedure of Example 8 is essentially repeated. Instead of monomers 1a and 2a, 68.1280 g (0.23560 mol) of monomer 1j is dehydrochlorinated in an "initial" solution of 320.7 g PPA having a P₂ O₅ content of 77.2% (prepared by mixing 96.2 g of 85.4% H₃ PO₄ with 224.5 g of 115% PPA). When dehydrochlorination is substantially complete, 57.824 g (0.23560 mol) of monomer 2j is added followed by the gradual addition of 126.9 g of P₂ O₅. The mixture is then stirred and heated essentially according to Example 8. The amount of P₂ O₅ is preselected (as determined in accord with the aforementioned formulae a* and b*) to provide the reaction mixture with an effective P₂ O₅ content of approximately 83.7% prior to the start of polymerization and an effective P₂ O₅ content of approximately 82.2% subsequent to substantially complete polymerization. The reaction product obtained exhibits stir-opalescence and is further characterized as having a polymer concentration of 18%; fibers are readily formed by direct spinning, or drawing from the reaction product. The polymer obtained is of the following structure:

    --AM--.sub.n

characterized by an intrinsic viscosity of 15 dL/g in MSA at 30° C.

EXAMPLE 25

The procedure of Example 8 is essentially repeated. Instead of monomers 1a and 2a, 68.1280 g (0.23560 mol) of monomer 1k is dehydrochlorinated in an "initial" solution of 320.64 g PPA having a P₂ O₅ content of 77.2% (prepared by mixing 96.19 g of 85.4% H₃ PO₄ with 184.4 g of 115% PPA). When dehydrochlorination is substantially complete, 57.0824 g (0.23560 mol) of monomer 2j is added followed by the gradual addition of 126.88 g of P₂ O₅. The mixture is then stirred and heated essentially according to Example 8. The amount of P₂ O₅ is preselected (as determined in accord with the aforementioned formulae a* and b*) to provide the reaction mixture with an effective P205 content of approximately 83.7% prior to the start of polymerization and an effective P205 content of approximately 82.2% subsequent to substantially complete polymerization. The reaction product obtained exhibits stir-opalescence and is further characterized as having a polymer concentration of 18%; fibers are readily formed by direct spinning, or drawing from the reaction product. The polymer obtained is of the following structure:

    --AN--.sub.n

characterized by an intrinsic viscosity of 14 dL/g in MSA at 30° C.

Analogous to the foregoing Examples 6-25, other Type I extended chain polymers may be synthesized to yield liquid-crystalline compositions having varying proportions of polymer concentration, P₂ O₅ content and polymer intrinsic viscosity in accordance with the present invention.

The synthesis is illustrated by the reaction systems in Tables 16a, 16b, 17a, 17b, and 17c. The m→, e→, and p→ denote most preferred, especially preferred, and preferred selected monomer reactions respectively.

                  TABLE 16a                                                        ______________________________________                                         Polymers of Type I, Class 1                                                    Polymerization Reactions:                                                       ##STR212##                                                                     ##STR213##                                                                     Monomer (1,2)                                                                            +     Monomer (2,1)                                                                              ##STR214##                                                                             Polymer I(1)                              ______________________________________                                          1a        +     2e                                                                                         ##STR215##                                                                             [AJ] .sub.n                                1a        +     2f                                                                                         ##STR216##                                                                             [AJ] .sub.n                                1a        +     2i                                                                                         ##STR217##                                                                             [AK] .sub.n                                1a        +     2k                                                                                         ##STR218##                                                                             [AB] .sub.n                                1a        +     2l                                                                                         ##STR219##                                                                             [AC] .sub.n                                1a        +     2m                                                                                         ##STR220##                                                                             [AD] .sub.n                                1a        +     2n                                                                                         ##STR221##                                                                             [AE] .sub.n                                1a        +     2o                                                                                         ##STR222##                                                                             [AF] .sub.n                                1a        +     2p                                                                                         ##STR223##                                                                             [AG] .sub.n                                1a        +     2q                                                                                         ##STR224##                                                                             [AH] .sub.n                                1a        +     2t                                                                                         ##STR225##                                                                             [AICI] .sub.n                              1a        +     2u                                                                                         ##STR226##                                                                             [AIDI] .sub.n                              1a        +     2v                                                                                         ##STR227##                                                                             [AIEI] .sub.n                              1a        +     2w                                                                                         ##STR228##                                                                             [AIFI] .sub.n                              1a        +     2x                                                                                         ##STR229##                                                                             [AIGI] .sub.n                              1a        +     2y                                                                                         ##STR230##                                                                             [AIHI] .sub.n                              1b        +     2e                                                                                         ##STR231##                                                                             [BJ] .sub.n                                1b        +     2i                                                                                         ##STR232##                                                                              [BK] .sub.n                               1b        +     2k                                                                                         ##STR233##                                                                             [B] .sub.n                                 1b        +     2l                                                                                         ##STR234##                                                                             [BC] .sub.n                                1b        +     2m                                                                                         ##STR235##                                                                             [BD] .sub.n                                1b        +     2m                                                                                         ##STR236##                                                                             [BD] .sub.n                                1b        +     2n                                                                                         ##STR237##                                                                             [BE] .sub.n                                1b        +     2o                                                                                         ##STR238##                                                                             [BF] .sub.n                                1b        +     2p                                                                                         ##STR239##                                                                             [BG] .sub.n                                1b        +     2q                                                                                         ##STR240##                                                                              [BH] .sub.n                               1b        +     2t                                                                                         ##STR241##                                                                             [BICI] .sub.n                              1b        +     2u                                                                                         ##STR242##                                                                             [BIDI] .sub.n                              1b        +     2v                                                                                         ##STR243##                                                                             [BIEI] .sub.n                              1b        +     2w                                                                                         ##STR244##                                                                             [BIFI] .sub.n                              1b        +     2x                                                                                         ##STR245##                                                                             [BIGI] .sub.n                              1b        +     2y                                                                                         ##STR246##                                                                             [BIHI] .sub.n                              1c        +     2a                                                                                         ##STR247##                                                                             [CI] .sub.n                                1c        +     2e                                                                                         ##STR248##                                                                              [CJ] .sub.n                               1c        +     2i                                                                                         ##STR249##                                                                             [CK] .sub.n                                1c        +     2k                                                                                         ##STR250##                                                                             [BC] .sub.n                                1c        +     2l                                                                                         ##STR251##                                                                             [C] .sub.n                                 1c        +     2m                                                                                         ##STR252##                                                                             [CD] .sub.n                                1c        +     2n                                                                                         ##STR253##                                                                             [CE] .sub.n                                1c        +     2o                                                                                         ##STR254##                                                                             [CF] .sub.n                                1c        +     2p                                                                                         ##STR255##                                                                             [CG] .sub.n                                1c        +     2q                                                                                         ##STR256##                                                                              [CH] .sub.n                               1c        +     2u                                                                                         ##STR257##                                                                             [CIDI] .sub.n                              1c        +     2v                                                                                         ##STR258##                                                                             [CIEI] .sub.n                              1c        +     2w                                                                                         ##STR259##                                                                             [CIFI] .sub.n                              1c        +     2x                                                                                         ##STR260##                                                                             [CIGI] .sub.n                              1c        +     2y                                                                                         ##STR261##                                                                             [CIHI] .sub.n                              1d        +     2a                                                                                         ##STR262##                                                                             [DI] .sub.n                                1d        +     2e                                                                                         ##STR263##                                                                             [DJ] .sub.n                                1d        +     2i                                                                                         ##STR264##                                                                              [DK] .sub.n                               1d        +     2m                                                                                         ##STR265##                                                                             [D] .sub.n                                 1d        +     2n                                                                                         ##STR266##                                                                             [DE] .sub.n                                1d        +     2o                                                                                         ##STR267##                                                                             [DF] .sub.n                                1d        +     2p                                                                                         ##STR268##                                                                             [DG] .sub.n                                1d        +     2q                                                                                         ##STR269##                                                                             [DH] .sub.n                                1d        +     2v                                                                                         ##STR270##                                                                             [DIEI] .sub.n                              1d        +     2w                                                                                         ##STR271##                                                                             [DIFI] .sub.n                              1d        +     2x                                                                                         ##STR272##                                                                              [DIGI] .sub.n                             1d        +     2y                                                                                         ##STR273##                                                                             [DIHI] .sub.n                              1e        +     2a                                                                                         ##STR274##                                                                             [EI] .sub.n                                1e        +     2e                                                                                         ##STR275##                                                                             [EJ] .sub.n                                1e        +     2i                                                                                         ##STR276##                                                                             [EK] .sub.n                                1e        +     2n                                                                                         ##STR277##                                                                             [E] .sub.n                                 1e        +     2o                                                                                         ##STR278##                                                                             [EF] .sub.n                                1e        +     2p                                                                                         ##STR279##                                                                             [EG] .sub.n                                1e        +     2q                                                                                         ##STR280##                                                                              [EH] .sub.n                               1e        +     2w                                                                                         ##STR281##                                                                             [EIFI] .sub.n                              1e        +     2x                                                                                         ##STR282##                                                                             [EIGI] .sub.n                              1e        +     2y                                                                                         ##STR283##                                                                             [EIHI] .sub.n                              1f        +     2a                                                                                         ##STR284##                                                                             [FI] .sub.n                                1f        +     2e                                                                                         ##STR285##                                                                             [FJ] .sub.n                                1f        +     2i                                                                                         ##STR286##                                                                             [FK] .sub.n                                1f        +     2o                                                                                         ##STR287##                                                                             [F] .sub.n                                 1f        +     2p                                                                                         ##STR288##                                                                              [FG] .sub.n                               1f        +     2q                                                                                         ##STR289##                                                                   it is understood that these      average values are meant for exemplary purposes, and may vary according to      instrument design, tests to be performed, or other factors. If acceptable      values for the channel means cannot be achieved, the operator may have to      return to the alignment procedures for the instrument described in      conjunction with FIG. 2.

Having adjusted the PMT's and performed alignment of the optical elements of the instrument, another adjustment may be made in establishing the calibration of the instrument. This additional adjustment relates to compensation for spectral cross-talk or overlap in the event that two-color fluorescence analysis is to be performed. This procedure facilitates the adjustment for fluorescence compensation so that undesired green signal will be removed from the red (PE stained) population, and undesired red signal will be removed from the green (FITC stained) population.

To perform the fluorescence compensation procedures, the operator preferably starts with a tube of calibration particles similar to that prepared with respect to the sensitivity test described above. This tube is prepared with a 1:1:1 mixture of FITC, PE and unlabeled beads by adding one drop of each of the three reagents, from the above-described containers, to three milliliters of sterile PBS. When this tube is inserted into the analyzer instrument, and in conjunction with the software program for calibration procedures, the screen displays a real-time dot plot, representing uncompensated fluorescence, such as seen in FIG. 4(a). The three separate dot populations displayed in FIG. 4(a) represent the unstained, green and red stained calibration beads. Unstained beads are typically located inside the square in the lower left corner of the display, illustrated by region 28. Red (PE stained) beads are typically located above the unstained population, indicated by region 30. The green population is to the right of the unstained population, indicated by region 32. Until fluorescence compensation is provided for on the instrument, the location of regions 28,30 and 32 are only approximate. Below the dot plot of FIG. 4(a) is a digital display of FL 1 compensation and FL 2 compensation. If these digital values are not fluctuating at or close to zero, adjustments should be made for fluorescence compensation.

Compensation is provided for two-color fluorescence analysis by adjusting FL 1 compensation and FL 2 compensation controls on the instrument until the compensation values listed on the screen are as close to zero as possible. After adjustment is made, the compensation value should fluctuate and vary equally above and below zero. With respect to FL 1 compensation, the compensated value represents the difference between the mean horizontal channel for the unstained population and the mean horizontal channel for the green stained population. As the FL 1 compensation control is adjusted on the instrument and the value on the screen approaches zero, the green population 32 on the dot plot should move downwardly until it is even with the unstained population 28 on a horizontal line parallel to the horizontal axis, as seen in FIG. 4(b).

In similar fashion, the mean channel difference listed next to FL 2 compensation on the screen represents the difference between the mean vertical channel for the unstained and red stained populations. As the FL 2 compensation control is adjusted on the instrument and the value on the screen approaches zero, the red population 30 on the dot plot should move horizontally until it is even with the unstained population 28 on a vertical line parallel to the vertical axis, as illustrated in FIG. 4(b). These adjustments of the FL 1 and FL 2 controls achieve fluorescence compensation by electrically subtracting a proportion of the unwanted green signal from the red population, and by electrically subtracting a proportion of the unwanted red signal from the green population. Compensation is achieved when the predetermined values of fluorescence compensation on the screen, set by the computer program at zero, are met. If acceptable or target settings cannot be achieved, the operator may be required to return to the alignment and PMT adjustment procedures as explained above.

Once alignment, PMT adjustment and fluorescence compensation have been completed, the operator may return to the sensitivity test described above in conjunction with FIG. 1. If the minimum separation values are achieved for each of the parameters being calibrated, the operator can proceed to use the instrument with full reliance that it is properly calibrated for the tests to be conducted.

Regarding the calibration particles to be utilized for the instantly described calibration procedures, a variety of particles may be used as standards. For instance, biological samples such as particles or cells may be employed as long as these samples either have, or may be treated to have, characteristics similar to the actual particles to undergo analysis. Along these lines, chicken red blood cells may be employed with proper selection techniques. A modified form of chicken red blood cells may be used as particle standards. Specifically, fluorescently labeled osmiumtetroxide-fixed chicken red blood cells may serve as particle standards since they have the size and scatter properties of biological cells. Moreover, osmiumtetroxide fixation quenches the autofluorescence of cells. These cells may be biotinilated, and subsequently reacted with a fluorophore conjugated to avidin in known fashion. Fluorescence of the avidin complex, bound to the cells, is not quenched by the osmiumtetroxide on the cells. The specific fluorophore conjugated to the avidin has spectral properties characteristic for cell-surface staining. Many different fluorophores may be used in the conjugates, including those to be described below.

The most preferred type of calibration particles for the present invention are plastic microbeads. Such beads may be fabricated with substantially uniform diameter, and have surface characteristics which are suitable for surface binding of fluorophores or other colorimetric marking agents. Substantially spherical beads may be formed having a diameter between 0.5 and 20 microns, and most preferably between 2 and 8 microns, so that these calibration beads are of the same order of magnitude in size as leucocytes. While the beads are usually made in solid form, they may be hollow inside and could be vesicles, such as liposomes or other microcarriers. Moreover, the beads do not have to be perfect spheres in order to function in accordance with the present invention. Plastic materials such as polystyrene, polyacrylamide and other latex materials may be employed for fabricating the beads, and other plastic materials such as polyvinylchloride, polypropylene and the like may also be utilized. Besides the fluorescein and the phycoerythrin labels for the beads described above, other fluorescence labels, such as allophycocyanin, Texas red, rhodamine, rhodamine-type compounds and other stains may be employed as fluorescent labels for purposes of the present invention. In preparing a kit of these reagents for calibration of instruments, the beads, whether labeled or unlabeled, are preferably provided as an aqueous solution so that the beads are present in concentrations ranging from 10⁵ to 10⁸ particles per milliliter, and preferably having a concentration of at least 10⁶ particles per milliliter.

While the calibration procedures were described above with specific reference to a flow cytometry instrument, no such limitation is intended for the present invention. Indeed, the calibration procedures of the present invention are applicable to instruments which analyze non-moving particles as well as moving particles. Various microscopes, such as fluorescence, automated, and quantitative microscopes, as well as image analyzers may be calibrated in accordance with the present invention.

Thus, the present invention provides a method and materials for calibrating an instrument prior to using that instrument for obtaining at least one light-related signal from particles under analysis. The present invention may be used with appropriate software to display minimum values of signal to noise ratios which should be met in order to determine that the instrument is calibrated for a specific light-related parameter. By reporting the signal to noise ratio as a differential on the linear scale, operator convenience is not only facilitated, but guesswork, eyeballing and errors are substantially reduced or eliminated. The techniques and materials of this invention also provide quality assurance for clinical diagnostic applications. 

What is claimed is:
 1. A method for calibrating a flow cytometry instrument for using said instrument to obtain at least one light-related signal from particles passing through the instrument for analysis comprising:passing calibration particles, having characteristics of like nature to particles expected to be tested, in a liquid flow stream so that each calibration particle passes, substantially one at a time, through an incident beam of light; detecting a light signal from the calibration particles passing through said beam of light; detecting a noise signal from the calibration particles passing through said beam of light; determining the ratio of the level of detected light signal to the level of detected noise signal; reporting said ratio as a measured separation value between the light signal and the noise signal; comparing said measured separation value to a predetermined separation value which represents a threshold for minimum instrument performance; and adjusting, if the predetermined separation value has not been attained, the operation of the instrument, while the calibration particles are passing therethrough, until the measured separation value reaches said predetermined separation value whereby the instrument is calibrated for subsequently analyzing particles.
 2. The method of claim 1 wherein said calibration particles are substantially spherical beads.
 3. The method of claim 2 wherein said beads have a diameter between 0.5 and 20 microns.
 4. The method of claim 3 wherein the diameter of said beads is between 2 and 8 microns.
 5. The method of claim 2 wherein said beads are made of plastic material.
 6. The method of claim 5 wherein said plastic material is selected from the group of plastics consisting of styrene, acrylamide, propylene and vinylchloride.
 7. The method of claim 1 wherein said calibration particles are chicken red blood cells.
 8. The method of claim 1 wherein said calibration particles are capable of emitting fluorescence at a known wavelength and the light-related signal for which the instrument is to be calibrated is said known wavelength of fluorescence.
 9. The method of claim 8 wherein said calibration particles are fluorescently-labeled osmiumtetraoxide-fixed chicken red blood cells.
 10. The method of claim 1 wherein said calibration particles are capable of emitting fluorescence at a plurality of known wavelengths and the light-related signal for which the instrument is to be calibrated is each of the plurality of known wavelengths of fluorescence.
 11. The method of claim 1 wherein said calibration particles are unlabeled so as to be substantially incapable of emitting fluorescence.
 12. The method of claim 1 wherein said calibration particles are included in a mixture wherein two particle species are labeled with different fluorescence agents and another particle species is unlabeled so that two fluorescence signals are calibrated, said unlabeled particles serving as the medium to introduce a noise signal which is detected to establish the signal to noise ratio for each fluorescence signal.
 13. The method of claim 12 wherein the adjusting step includes compensating each fluorescent signal by substantially eliminating spectral overlap.
 14. The method of claim 13 wherein said compensating step includes electrically subtracting a proportion of the first fluorescent light signal from the second fluorescent light signal and electrically subtracting a proportion of the second fluorescent light signal from the first fluorescent light signal.
 15. The method of claim 14 further including displaying the uncompensated fluorescence signals in a dot-population display wherein a first group of dots represents the first fluorescent light signal and a second group of dots represents the second fluorescent light signal.
 16. The method of claim 15 wherein said dot population display includes a digital readout of compensation values for said first and said second fluorescent light signals, said adjusting step including the adjustment of the compensation values until a predetermined compensation value is reached for each fluorescent light signal whereby each fluorescent light signal is compensated.
 17. The method of claim 12 wherein the fluorescently-labeled calibration particles and the unlabeled calibration particles are provided in substantially equal amounts in a carrier liquid which is used to form said liquid flow stream containing the calibration particles.
 18. The method of claim 1 wherein said reporting step includes displaying said ratio in a form visible to an operator performing the calibration method.
 19. The method of claim 18 wherein said reporting step includes displaying a histogram for the light signal being detected, said histogram showing the light signal mean channel and the noise signal mean channel.
 20. The method of claim 19 wherein said reporting step includes displaying, in digital readout form, the value of the light signal mean channel, the value of the noise signal mean channel, the separation value between the light signal mean channel and the noise signal mean channel representing said signal to noise ratio, and said predetermined separation value representing said threshold for minimum instrument performance.
 21. The method of claim 20 wherein said reporting step includes displaying a plurality of histograms, each for a different light-related signal being detected, and further displaying said digital readout values associated with each different histogram of light-related signals.
 22. The method of claim 21 wherein said reporting step includes displaying three histograms and associated digital readout values for detecting three different light-related signals, two of said light signals being fluorescence at different wavelengths, the third signal being a light scatter signal.
 23. The method of claim 1 wherein said reporting step expresses the ratio as a linearized difference between the light signal and the noise signal.
 24. The method of claim 1 wherein the adjusting step includes adjusting detectors to positions which improve receipt of the respective signals which are detected.
 25. A method for calibrating an instrument for using said instrument to obtain at least one light-related signal from particles under analysis comprising:directing an incident beam of light at calibration particles having one or more known characteristics related to particles expected to be analyzed; detecting a light signal from the calibration particles; detecting a noise signal from the calibration particles; measuring the ratio of the level of detected light signal to the level of detected noise signal and reporting same; comparing said measured ratio to a predetermined ratio which represents a threshold for minimum instrument performance; and adjusting, if the predetermined ratio has not been attained, the operation of said instrument, while the calibration particles are within the incident beam of light, until the measured ratio reaches said predetermined ratio whereby the instrument is calibrated for subsequently analyzing particles.
 26. The method of claim 25 wherein said calibration particles include labeled particles and unlabeled particles, and wherein the detected light signal is associated with said labeled particles and the detected noise signal is associated with said unlabeled particles.
 27. The method of claim 25 wherein said ratio is reported as a linearized separation value between the light signal and the noise signal.
 28. A method for calibrating a flow cytometry instrument for using said instrument to obtain at least two different fluorescence signals from particles passing through the instrument for analysis comprising:passing substantially spherical calibration beads in a liquid flow stream so that each bead passes, substantially one at a time, through an incident beam of light, said beads being labeled with two different fluorochromes and provided in substantially equal amounts in a carrier liquid which is used to form said flow stream; detecting each of the two fluorescence signals from the beads passing through said beam of light; detecting noise signals associated with each of the two fluorescence signals, the unlabeled beads providing the noise signal for each of the two fluorescence signals; determining the ratio of the level of detected fluorescence signal to the level of detected noise signal for each of the two fluorescence signals; displaying said ratio for each of the two fluorescence signals as a measured separation value between each respective light signal and the noise signal, said displaying step utilizing a log scale relationship in which the ratio of signal to noise is expressed by the mean channel linear difference between the light signal and the noise signal; comparing said measured separation value for each of the two fluorescence signals to predetermined separation values each of which represents a threshold for minimum instrument performance; and adjusting, if the predetermined separation values for either of the two fluorescence signals has not been attained, the operation of the instrument while the calibration beads are passing therethrough until each measured separation value reaches the predetermined separation value, whereby the instrument is calibrated for subsequently obtaining said two fluorescence signals from particles to be analyzed. 